Such vehicle-washing stations generally include a bridge structure or portal frame serving as a support for cylindrical scrubbing brushes which rotate about substantially horizontal and vertical axes while contacting the body of the vehicle to be cleaned; see, for example, my prior U.S. Pat. Nos. 3,793,667 and 3,688,329. The portal frame and the vehicle move relatively to each other during the cleaning operation, along a predetermined path, with the portal frame traveling along a track while the vehicle is standing still or, conversely, with the vehicle entrained by a chain or the like past the stationary frame. These body-scrubbing brushes, however, cannot clean the vehicle wheels which are generally recessed in respective housings or wells below their fenders.
There are already known a number of wheel-cleaning devices using rotary brushes that are carried on horizontal shafts which in operation are aligned with the respective wheel axles. In some of these instances, the wheel-scrubbing brushes are actuated by sensors designed to detect the alignment of a vehicle wheel with the device. Such a sensor may be a flexible rod extending transversely to the path of relative vehicle motion across the course of the wheels to be scrubbed, a signal generated upon the deflection of the rod by an oncoming wheel serving to arrest the portal-frame or vehicle drive and to advance the wheel-scrubbing brush into operative engagement with the confronting vehicle wheel. A drawback of this arrangement is that the rod, lying necessarily at a relatively low level above the ground, may be tripped accidentally by an object other than a vehicle wheel and may therefore cause untimely triggering of the wheel-cleaning device. There is also the danger that the flexible rod may be dragged down by the tire and get caught between the wheel and the ground (or possibly the driving chain entraining the vehicle) with resulting breakdown of the system.
Other known wheel-cleaning devices dispense with a separate sensor and use brushes which are biased under light pressure against the passing vehicle body in order to enter the well of a wheel arriving in its aligned position; the forward motion of the brush then actuates its drive motor to start the cleaning operation. Although such an arrangement obviates the aforementioned drawbacks, its disadvantage lies in the fact that the wheel-scrubbing brush must scrape the sides of the vehicle body before and after operating on a wheel. This scraping action, especially if the car is very dirty, may lead to scratches and abrasions of the vehicular coating.